CVT Target Engine Speed Control with Unreliable Output Feedback

ABSTRACT

A machine may include an engine, a traction device, a continuously variable transmission (CVT) connecting the engine to the traction device, an operator input device outputting engine output command signals input by an operator, an engine speed sensor monitoring an engine output speed, and an electronic control module (ECM). The ECM controls a machine output of the machine by executing a transmission output control routine using transmission output parameters as feedback when transmission output parameter sensor signals are reliable. The ECM controls the machine output by executing a target engine speed control routine using an engine output speed sensor signals as feedback when the transmission output parameter sensor signals are nor reliable. In the target engine speed control routine, the ECM determines a CVT transmission ratio that will cause the CVT to apply a load to the engine that will cause the engine to run at the target engine speed.

TECHNICAL FIELD

The present invention relates generally to speed control in vehicles andmachines, and more particularly, to controlling an engine speed and atransmission ratio in a vehicle or machine having a continuouslyvariable transmission by comparing an actual engine speed to a targetengine speed when machine brakes are applied, transmission outputsensors fail or other conditions exist making transmission control basedon transmission output conditions unreliable.

BACKGROUND

Transmission systems may be used to couple the output of a prime moveror power source, for example, an internal combustion engine, to a drivenelement or device such as wheels or a work implement on a work machine.Transmissions are typically part of a power train that transmits powerthat may be in the form of torque and/or rotational speed from the powersource to the driven element. A continuously variable transmission (CVT)provides an infinite or continuous range of torque-to-speed outputratios with respect to any given input from the power source. In otherwords, the output of the CVT can be increased or decreased across acontinuous range in infinitesimally small increments.

U.S. Pat. No. 8,216,109 issued on Jul. 10, 2012, to Dahl et al. entitled“Torque-Based Control System for a Continuously Variable Transmission”discloses a method of managing the operation of a machine having anoperator station with one or more operator interface devices, one ormore traction devices and a power train operatively connected to driveat least one of the traction devices. The operator interface devices mayinclude devices for initiating movement of the machine by transmittingsignals to a control module. The power train includes a power source,such as an engine, and a transmission unit connected to receive thepower output from the power source and transmit the power output to thetraction devices. The control module regulates the operation of thetransmission unit in response to one or more inputs from the operatorinterface devices. A first sensor associated with the power sourcesenses an output speed thereof, and a second sensor associated with thetransmission unit and/or the traction device senses a travel speed ofthe machine. The transmission unit may embody a continuously variabletransmission. The control module uses information provided by thesensors to control an output torque of the transmission unit that isdetermined in response to multiple inputs by an operator at the operatorinterface devices.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a machine for operating at awork site and traveling over a work surface of the work site isdisclosed. The machine may include an engine, a traction device, acontinuously variable transmission (CVT) operatively connected betweenthe engine and the traction device to transfer power output by theengine to the traction device, operator input devices in an operatorstation of the machine for detecting engine output commands and brakeforce commands that are input by an operator of the machine andoutputting engine output command signals corresponding to the engineoutput commands and brake force command signals corresponding to thebrake force commands input by the operator at the operator inputdevices, a transmission output parameter sensor automatically monitoringa transmission output parameter of the CVT and outputting transmissionoutput parameter sensor signals corresponding to the transmission outputparameter of the CVT, an engine speed sensor automatically monitoring anengine output speed of the engine and outputting engine speed sensorsignals corresponding to the engine output speed of the engine, and anelectronic control module (ECM) operatively connected to the engine, theCVT, the operator input devices, the engine speed sensor and thetransmission output parameter sensor. The ECM is programmed to receivethe engine output command signals and the brake force command signalsfrom the operator input devices, and execute a transmission outputcontrol routine based on the engine output command signals and thetransmission output parameter sensor signals to control a machine outputof the machine in response to determining that the transmission outputparameter sensor signals from the transmission output parameter sensorare a reliable indicator of transmission output conditions. In responseto determining that the transmission output parameter sensor signalsfrom the transmission output parameter sensor are not the reliableindicator of the transmission output conditions, the ECM is furtherprogrammed to determine a transmission control target engine speed basedon the engine output command signals, determine a transmission ratio forthe CVT based on the transmission control target engine speed to causethe engine to operate at the transmission control target engine speed,and transmit transmission command signals to the CVT to control the CVTso that a transmission output speed divided by a transmission inputspeed is equal to the transmission ratio determined based on thetransmission control target engine speed.

In another aspect of the present disclosure, a method for controlling anengine output speed of an engine of a machine is disclosed. The machineincludes a traction device and a continuously variable transmission(CVT) operatively connected between the engine and the traction deviceto transfer power output by the engine to the traction device to propelthe machine over a work surface of a work site. The method may includereceiving engine output command signals and brake force command signalsfrom an operator of the machine indicating a commanded machine functionand a commanded brake force, respectively, input by the operator, andperforming a transmission output control routine based on the engineoutput command signals and the transmission output parameter sensorsignals to control a machine output of the machine in response todetermining that transmission output parameter sensor signals are areliable indicator of transmission output conditions. In response todetermining that the transmission output parameter sensor signals arenot the reliable indicator of the transmission output conditions, themethod further includes determining a transmission control target enginespeed based on the engine output command signals, determining atransmission ratio for the CVT based on the transmission control targetengine speed to cause the engine to operate at the transmission controltarget engine speed, and transmitting transmission command signals tothe CVT to control the CVT so that a transmission output speed dividedby a transmission input speed is equal to the transmission ratiodetermined based on the transmission control target engine speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary vehicle or machine that can travelover a work surface;

FIG. 2 is a schematic view of mechanical, electrical and controlcomponents of a power train of the vehicle of FIG. 1;

FIG. 3 is a graph of power versus engine speed with an exemplary lugcurve for an engine of the vehicle of FIG. 1;

FIG. 4 is a block diagram of a CVT transmission control strategyselection routine in accordance with the present disclosure that may beexecuted by an electronic control module of the vehicle of FIG. 1; and

FIG. 5 is a block diagram of a target engine speed CVT transmissioncontrol routine in accordance with the present disclosure that may beexecuted by an electronic control module of the vehicle of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary vehicle or machine 10 in the form of a largewheel loader that may traverse a work surface at a work site. While awheel loader is shown, the CVT target engine speed control strategydiscussed herein may be implemented in any other appropriate type ofwork vehicle or machine. The machine 10 includes a frame 12 supporting amachine body 14, and with the frame 12 being supported above the worksurface by traction devices 16. As illustrated, the traction devices 16include a plurality of wheels 16, but the traction devices 16 could beany other appropriate devices such as an undercarriage with tracks,halftracks, or combinations of tracks, wheels or other traction devices.

The machine 10 is driven by a power train including an engine 18operatively connected to a CVT 20 that in turn is operatively connectedto the wheels 16. The CVT 20 transfers power generated by the engine 18to the wheels 16 to rotate the wheels 16 and propel the machine 10 overthe work surface. The CVT 20 may be any automatic transmission that canchange seamlessly through a continuous range of effective gear ratios.For example, the CVT 20 may be a hydrostatic CVT having a variabledisplacement pump pumping hydraulic fluid to either a constantdisplacement or variable displacement hydraulic motor, with the variabledisplacement pump having a swash plate that is adjusted to vary the flowthrough the pump and, correspondingly, the gear ratio of the CVT 20 andthe load on the engine 18. Alternatively, the CVT 20 could be a variablediameter pulley CVT, a toroidal CVT, a cone CVT or the like providingcontinuous adjustment through a range of gear ratios.

An operator can control the movement of the machine 10 along with otheroperations of the machine 10 at an operator station 22. The controlledoperations can include speed control, steering, load dumping, actuationof implements of the machine 10, and the like. The operator station 22may have a plurality of operator input devices 24 for inputting commandsfor the engine 18, the CVT 20 and other systems of the machine 10. Theoperator input devices 24 can include engine throttles, brake pedals,gear shift levers, steering wheels, implement lift and articulationcontrols, graphical user interfaces, and the like. Sensors associatedwith each of the operator input devices 24 detect manipulation of theoperator input devices 24 by an operator and transmit correspondinginput device command signals that are received and processed by anelectronic control module (ECM) 26. Particularly relevant to the presentdisclosure are engine output command signals transmitted from an enginethrottle or the like, or a combination of operator input devices 24 thatmay cause the engine 18 to operate according to conventional enginecontrol strategies, and CVT output command signals that may be evaluatedby the ECM 26 using an appropriate transmission control strategy todetermine a CVT transmission operating state that will cause the CVT 20to operate with the desired output indicated by the operator. When theECM 26 executes a transmission output control strategy, the ECM 26 maymonitor a desired transmission output parameter indicative of thetransmission output conditions, such as, for example, a transmissionoutput speed TOS or a transmission output torque TOT, and use thefeedback signal for the monitored transmission output parameter tocontrol the CVT 20 to produce the desired machine output indicated bythe operator. When the ECM 26 executes an engine speed control strategy,the ECM 26 may determine a target engine speed TES and corresponding CVTtransmission ratio TR that will cause the CVT 20 to apply a load to theengine 18 based on a current transmission output speed TOS that willcause the engine 18 to run at the target engine speed TES as the machine10 accelerates, decelerates or maintains speed as commanded by theoperator. The conditions under which the ECM 26 executes either thetransmission output control strategy or the target engine speed controlstrategy, and exemplary routine for executing the target engine speedcontrol strategy, are discussed further below.

The machine 10 also collects and records operational data relating tothe operation of the machine 10 as it operates within the work site andtraverses the work surface. The machine 10 may include a variety ofsensors 28 operating independently or as components of other control andmonitoring systems to automatically monitor various operational dataduring travel of the machine 10 over the work surface and theperformance of machine operations within the work site. The sensors 28monitoring the operational data may include speed sensors detectingmachine, engine and transmission speeds, and torque sensors sensingtorque at various points along the power train and/or rolling resistanceof the wheels 16. The sensors 28 may also include payload weight sensorsdetecting the weight of a load carried by the machine 10, pressuresensors for suspension cylinder and lift cylinder pressures, and thelike. The operational data monitored by the sensors 28 may also includeroad parameters such as, for example, the grade of the road over whichthe machine 10 is traveling measured by inertial measuring units (IMUs),accelerometers or inclinometers, and the location coordinates andelevation of the machine 10 at a given time as detected by globalpositioning system (GPS) receivers. Some operational data may bemonitored directly, while other data may be derived or calculated fromthe monitored parameters.

The operator input devices 24, the ECM 26 and the sensors 28 arecomponents of a machine control system for the machine 10. Referring toFIG. 2, an exemplary arrangement of mechanical, electrical and controlcomponents of the power train of the machine 10 is shown with thevarious control components integrated into the power train controlsystem. The engine 18 may be configured to receive the engine outputcommands from the operator input devices 24 and operate with thecommanded engine output CEO in response. The engine 18 may beconventional and may include a mechanical governor, an electronicgovernor implemented in software, or other appropriate conventionalengine output control mechanism and control strategy. The engine 18further includes an engine output shaft 30 operatively connected at aninput end of the CVT 20. The engine output shaft 30 may be directlyconnected to the CVT 20, or connected through an intermediate powertransfer device such as a clutch, and torque converter or the like.

The CVT 20 may include a CVT actuator 32 that operates to set or controlthe CVT 20 to achieve a desired ratio of a transmission output speed TOSto a transmission input speed TIS or to create a desired transmissionoutput torque TOT on the transmission output shaft 34 or a desired loadon the engine 18 through the engine output shaft 30 depending on the CVTtransmission control strategy being executed by the ECM 26. Theconfiguration of the CVT actuator 32 may vary based on the particulartype of CVT 20 implemented in the machine 10. For a hydrostatic CVT, theCVT actuator 32 may operate to rotate the swash plate of the variabledisplacement pump and/or a variable displacement motor. The hydrostaticCVT actuator 32 may be actuated by the ECM 26 by varying currenttransmitted to flow control valves of the CVT actuator 32 to move apiston or other component operatively coupled to the swash plate torotate the swash plate. Variable pulley actuators may control thespacing of sheaves of pulleys in a variable diameter pulley CVT to varythe gear ratio. The ECM 26 may similarly vary current or otherappropriate control signals to actuate the CVT actuator 32 and vary thespacing of the sheaves. In alternative embodiments, the CVT actuator 32may include a CVT actuator controller, and the ECM 26 may transmitappropriate control signals that are interpreted by the CVT actuatorcontroller that in turn will cause the CVT actuator 32 to actuate andadjust the CVT 20. At the output end of the CVT 20, a transmissionoutput shaft 34 may extend and be operatively connected to the wheels16. Similar to the engine output shaft 30, the transmission output shaft34 may have intermediate components such as clutches, differentials andthe like for transferring the power output from the CVT 20 to the wheels16.

The machine 10 further includes brakes 36 operably connected to thetransmission output shaft 34 for selectively applying brake force tocontrol the speed and momentum of the machine 10. The brakes 36 mayinclude a brake actuator 38 that is actuatable to adjust the brake forceapplied by the brakes 36. The brakes 36 and the brake actuator 38 may beconventional and may include a mechanical connection to thecorresponding operator input device(s) 24, an electrical connection tocontrol valves of the brake actuator 38, or other appropriateconventional actuation and control strategy for converting the operatorinput of a desired brake force into the application of brake force tothe transmission output shaft 34. In alternative embodiments, the brakeactuator 38 may include a brake actuator controller, and the ECM 26 maytransmit appropriate control signals with the commanded brake force CBFthat are interpreted by the brake actuator controller that in turn willcause the brake actuator 38 to actuate and adjust the brakes 36.

The ECM 26 may be capable of processing the information received fromthe operator input devices 24 and the sensors 28 using software storedat the ECM 26, and outputting command and control signals to the engine18 and the CVT actuator 32, and information to displays (not shown) inthe operator station 22. The ECM 26 may include a processor 40 forexecuting a specified program, which controls and monitors variousfunctions associated with the machine 10. The processor 40 may beoperatively connected to a memory 42 that may have a read only memory(ROM) 44 for storing programs, and a random access memory (RAM) 46serving as a working memory area for use in executing a program storedin the ROM 44. Although the processor 40 is shown, it is also possibleand contemplated to use other electronic components such as amicrocontroller, an application specific integrated circuit (ASIC) chip,or any other integrated circuit device. While the discussion providedherein relates to the functionality of a power train control system, theECM 26 may be configured to control other aspects of the operation ofthe machine 10 such as, for example, steering, dumping loads ofmaterial, actuating implements and the like. Moreover, the ECM 26 mayrefer collectively to multiple control and processing devices acrosswhich the functionality of the power train control system and othersystems of the machine 10 may be distributed. For example, the operatorstation 22, the engine 18, the CVT actuator 32 and/or the brake actuator38 may each have ECMs that communicate with the main ECM 26. Suchvariations in consolidating and distributing the processing of the ECM26 as described herein are contemplated as having use in engine speedcontrol in accordance with the present disclosure.

The operator input devices 24 are operatively connected to the ECM 26for two-way communications. The operator input devices 24 transmitrequests from the operator generated in response to the operatormanipulating the controls in the operation station 22, and in particularengine commands indicating an engine speed or engine power outputrequested by the operator and brake force commands indicating thedesired brake force to be applied by the brakes 36. The ECM 26 transmitsinformation to be provided to the operator at output devices (not shown)in the operator station 22. The output devices may be any devicescapable of providing a sensory perceptible output to the operator, suchas visual display devices, lamps, speakers, and the like. Theinformation communicated to the operator may include an engine speed, amachine speed, a bucket position, a load weight, a fuel level, anoperational mode indication, and the like.

The sensors 28 may encompass a variety of sensors that are configured tocollect operational data for the machine 10 and transmit sensor signalsto the ECM 26 that correspond to the measured values of the operationaldata. In particular, the sensors 28 discussed herein may collectoperational data that is useful in controlling the speed of the engine18 as the machine 10 travels through the work site. For example, thesensors 28 may include an engine speed sensor 48 and an engine torquesensor 50 operatively coupled to the engine output shaft 30. The enginespeed sensor 48 detects the rotational speed of the engine output shaft30, which corresponds to an engine output speed EOS of the engine 18.The engine torque sensor 50 detects a magnitude of an engine outputtorque EOT created by the engine output shaft 30 and transmitted to theCVT 20. Similarly, a transmission speed sensor 52 and a transmissiontorque sensor 54 are operatively coupled to the transmission outputshaft 34. The transmission speed sensor 52 detects a transmission outputspeed TOS of the transmission output shaft 34, and the transmissiontorque sensor 54 detects a magnitude of a transmission output torque TOTcreated by the transmission output shaft 34 and transmitted to thewheels 16. The engine speed sensor 48 and the transmission speed sensor52 transmit engine speed sensor signals and transmission speed sensorsignals, respectively, to the ECM 26 having values corresponding to theengine output speed EOS and the transmission output speed TOS, while theengine torque sensor 50 and the transmission torque sensor 54 transmitengine torque sensor signals and transmission torque sensor signals,respectively, to the ECM 26 having values corresponding to the engineoutput torque EOT and the transmission output torque TOT.

The performance of the engine 18 may be illustrated graphically in FIG.3. A graph 60 of the power versus the engine speed of the engine 18 hasa lug curve 62 representing the operation of the engine 18 at a constantthrottle amount. For example, the lug curve 62 may represent the 100%throttle engine response. The engine 18 will have a maximum or high idleengine speed at a point 64 where no load is applied to the engine outputshaft 30. As a load on the engine output shaft 30 is increased, thesteady state operating point of the engine 18 will move upward and tothe left on the lug curve 62 decreasing the engine output speed from itscurrent operating point. As the load on the engine output shaft 30 isdecreased, the steady state operating point of the engine 18 will movedownward and to the right on the lug curve 62 increasing the engineoutput speed from its current operating point.

The ECM 26 is operatively connected to the CVT actuator 32 to controlthe load applied by the CVT 20 on the engine 18, and correspondingly theengine output speed EOS, in response to the engine output commandsignals from the operator input devices 24. The operator will indicate adesire to increase, decrease or maintain a power output or output speedof the engine 18 by manipulating the appropriate operator inputdevice(s) 24 in the operator station 22. Appropriate sensors associatedwith the operator input device(s) 24 sense the manipulation of theoperator input device(s) 24 and transmit the engine output commandsignals with values corresponding to the manipulation of the operatorinput device(s) 24. Simultaneously, the ECM 26 receives the transmissionoutput command signals and determines the appropriate transmissionoperating state based on the output command signals.

In the machine 10 in accordance with the present disclosure under normaloperating conditions, the ECM 26 may execute the transmission outputcontrol strategy discussed above wherein the ECM 26 monitors the desiredtransmission output parameter for the transmission output conditions anduses the feedback signal for the monitored transmission output parameterto control the CVT 20 to produce the desire machine output indicated bythe operator through the engine output command signals. Strategies forperforming transmission output control are known to those skilled in theart, and the implementation of such known transmission output controlstrategies and later developed strategies in machines 10 in accordancewith the present disclosure are contemplated by the inventor. Normaloperating conditions for executing the transmission output controlstrategy exist when the brakes 36 are not being applied to create brakeforce on the transmission output shaft 34 and the transmission torquesensor 54 is functioning properly. Under these conditions, thetransmission output parameter(s) monitored by the appropriate sensor(s)28 and transmitted to the ECM 26 as feedback signals are an accurateindicator of the transmission output conditions at the CVT 20.

The transmission output control strategy works well during typicaloperation of the machine 10, but may have limitations under conditionswhere the transmission output feedback signals for the transmissionoutput parameter(s) are unreliable indicators of the actual conditionsat the transmission output. For example, when the operator lets off theengine throttle and applies the brakes 36 to slow the machine 10, theECM 26 may set target transmission output to zero or to a low idleoutput torque, while the brake force applied by the brakes 36 to thetransmission output shaft 34 influences the measurement of thetransmission output torque TOT measured by the transmission torquesensor 54 and used as the feedback signal by the ECM 26. Thetransmission output control strategy tries to adjust for incorrectlymeasured transmission output torque TOT that is being influenced by theapplication of the brakes 36. The situation can lead to instability asthe ECM 26 adjusts the CVT 20 to correct the falsely measuredtransmission output torque TOT while the brakes 36 are applying torqueto the transmission output shaft 34. As a further example, thetransmission output feedback signals will be unreliable when thetransmission torque sensor 54 is faulty or malfunctioning and is eithernot transmitting signals to the ECM 26 or transmitting signals that donot represent the actual transmission output torque TOT.

To handle these and other situations where the transmission outputfeedback is unreliable, the ECM 26 in accordance with the presentdisclosure may be configured to execute a target engine speed controlstrategy in place of the transmission output control strategy andcontrolling the CVT 20 using the engine output speed EOS as feedback tomaintain an approximately constant target engine speed TES. Under thetarget engine speed control strategy, the ECM 26 may use the engineoutput commands along with other operator inputs and/or operational datafrom the sensors 28 to determine the target engine speed TES and thecorresponding transmission ratio TR. The transmission control softwaredetermines the transmission ratio TR for the CVT 20 needed to apply aload on the engine 18 so that the engine 18 will run at the targetengine speed TES. The target engine speed TES may be determined in anyappropriate manner based on the engine operating requirements for aparticular implementation. In one embodiment, the target engine speedTES may be a predetermined engine speed stored at the ECM 26. The targetengine speed may be fixed for the machine 10, or may be updatable viaany appropriate mechanism such as operator input at one of the operatorinput devices 24. In alternative embodiments, the value of the targetengine speed TES may be mapped to one or more operator inputs. Forexample, the target engine speed TES may be determined based on theengine throttle commands from the operator. The target engine speed TESmay be proportional to the value of the engine throttle command so thatthe target engine speed TES has a maximum value at the 100% throttleposition and decreases as the displacement of the engine throttledecreases. The value of the target engine speed TES may be similarlyaffected by additional or alternative operator inputs as necessary.

Also under the target engine speed control strategy, the transmissionratio TR may be determined using the target engine speed TES determinedby the ECM 26 along with a current machine speed CMS of the machine 10.In the target engine speed control strategy in accordance with thepresent disclosure, the transmission ratio TR may be manipulated tocreate a load on the engine 18 at the current machine speed CMS thatwill force the engine 18 to operate at the target engine speed TES. Thetransmission ratio is equal to the transmission output speed TOS dividedby the transmission input speed TIS in the target engine speed controlstrategy. In calculating the transmission ratio TR, the transmissioninput speed TIS may have a value corresponding to the commanded targetengine speed TES. The transmission output speed TOS may be the sensorvalue transmitted by the transmission speed sensor 52, or any otherappropriate value reflecting the current machine speed CMS.

After determining the target engine speed TES and the transmission ratioTR, the ECM 26 will cause the CVT actuator 32 to actuate by varying acontrol current, transmitting control signals or otherwise communicatingwith the CVT actuator 32. The CVT actuator 32 in response actuates tocause the CVT 20 to have the CVT transmission ratio TR to force theengine output speed EOS to the target engine speed TES. This process maybe repeated over time to maintain the engine output speed EOSapproximately equal to the target engine speed TES.

FIG. 4 illustrates an exemplary CVT transmission control strategyselection routine 100 that may be stored in the memory 42 and executedby the ECM 26. The routine 100 is configured to determine whetherconditions exist that make the transmission output feedback signalsunreliable for use in the transmission output control strategy. If thefeedback signals are unreliable, the routine 100 will cause the ECM 26to execute the target engine speed control strategy. The routine 100evaluates the application of the brakes 36 and the operational status ofthe transmission torque sensor 54, but those skilled in the art willunderstand that other factors may exist that may render the transmissionoutput feedback signals unreliable, and evaluation of such factors bythe ECM 26 in the routine 100 is contemplated as having use in machines10 in accordance with the present disclosure.

The routine 100 starts at a block 102 where the ECM 26 receives theengine output commands and brake force commands transmitted from theoperator input devices 24 and determines the values of the engine outputcommands and the brake force commands input by the operator to cause themachine 10 to move over the work surface at varying speeds and withvarying power outputs. In some embodiments, the operator input devices24 may transmit engine output commands having values equal to zero ifthe operator has not operated any of the operator input devices 24. Inthese or other embodiments, if no engine output commands are detected,the ECM 26 may interpret the absence of engine output commands as acommanded engine output CEO of zero. When the engine output commandshave values of or are determined to be equal to zero, the ECM 26 maymaintain the engine 18 at a low idle speed if the machine 10 is notmoving, or handle coasting or braking of the machine 10 if the machine10 is moving over the work surface in the succeeding steps of theroutine 100. It should be noted that the engine output commands areconcurrently received by the engine 18 and the appropriate conventionalengine output control mechanism and control strategy will cause theengine 18 to operate at a corresponding engine speed or engine power.

The brake pedal or other brake input device (not shown) at the operatorstation 22 may have an associated brake input sensor (not shown) fordetecting movement of the brake input device and transmitting brakeforce command signals. The brake force command signals have valuesrepresenting the commanded brake force CBF that corresponds to theamount of displacement of the brake input device. If the commanded brakeforce CBF in the brake force command signals is greater than zero, theoperator is requesting brake force to apply torque to the transmissionoutput shaft 34 and reduce the momentum of the machine 10. It should benoted that the brake force commands are concurrently received by thebrake actuator 38 in the present embodiment and the appropriateconventional brake control mechanism and brake control strategy willcause the brakes 36 to apply the corresponding brake force to thetransmission output shaft 34.

After the commanded engine output CEO and the command brake force CBFare determined by the ECM 26 at the block 102, control may pass to ablock 104 where the ECM 26 determines whether the transmission outputfeedback signal is usable. Various conditions of the transmission torquesensor 54 may render the transmission output torque TOT signal unusableor unreliable, and the ECM 26 may be programmed to assess some or all ofthe conditions. For example, the ECM 26 may assess whether signals fromthe transmission torque sensor 54 are being received or have beencutoff. Such assessment may include determining whether a predeterminedtime period has elapsed since last receiving signals from thetransmission torque sensor 54 that may indicate that the transmissiontorque sensor 54 is not transmitting signals or that the connectionbetween the ECM 26 and the transmission torque sensor 54 has beensevered. In other implementations, the ECM 26 may be programmed totransmit a status request message to the transmission torque sensor 54to which the transmission torque sensor 54 will respond if thetransmission torque sensor 54 is functioning properly. In still otherimplementations, the ECM 26 or the transmission torque sensor 54 mayperiodically perform diagnostics on the transmission torque sensor 54 todetermine the operational status. Data from the diagnostics, includingan operational status of the transmission torque sensor 54, may bestored at the ECM 26 and evaluated by the ECM 26 at the time the routine100 is executed. If the ECM 26 determines that the signal from thetransmission torque sensor 54 is not usable at the block 104 using anyindividual assessment or combination of assessment tools, control maypass to a target engine speed CVT transmission control routine 300 wherethe target engine speed control strategy will be executed to control theCVT 20 as discussed further below.

If the ECM 26 determines that the signal from the transmission torquesensor 54 is usable at the block 104, control may pass to a block 106where the ECM 26 determines whether the brakes 36 are being applied. TheECM 26 may determine whether the commanded brake force CBF from theblock 102 is greater than zero. If the commanded brake force CBF isgreater than zero, application of the brakes 36 is being requested bythe operator, and the transmission output feedback signal may beunreliable for the reasons discussed above. Consequently, if thecommanded brake force CBF is greater than zero, control may pass to thetarget engine speed CVT transmission control routine 300 for executionof the target engine speed control strategy. If the commanded brakeforce CBF is not greater than zero, the brakes 36 are not being applied,and control may pass to a transmission output control routine 200 forexecution of the transmission output control strategy of the typediscussed above.

FIG. 5 illustrates a flow diagram for a target engine speed CVTtransmission control routine 300 that may be stored in the memory 42 andexecuted by the ECM 26 after the ECM 26 determines in the routine 100that the transmission output feedback signal is unreliable due toapplication of the brakes 36, failure or malfunctioning of thetransmission torque sensor 54 or other conditions. The routine 300 isconfigured so the ECM 26 can control the CVT 20 to maintain the engineoutput speed EOS approximately equal to the target engine speed TES overtime using the engine output speed signals from the engine speed sensor48 as feedback. In alternative implementations, the transmission outputspeed signals from the transmission speed sensor 52 are also used in thecontrol strategy. The control strategy works to drive the engine 18 tothe target engine speed TES by manipulating the transmission ratio TR ofthe CVT 20.

The routine 300 starts after the ECM 26 receives the engine outputcommands at the block 102 of the routine 100 and determines that thetransmission output feedback signals are unreliable. After theprocessing of the routine 100, control may pass to a block 302 where theECM 26 may determine a transmission control target engine speed TEScorresponding to the values in the engine output commands. The ECM 26may determine the target engine speed TES using any appropriate methodsuch as those described above. Subsequent to the determination of thetarget engine speed TES, control may pass to a block 304 where the ECM26 may calculate the transmission ratio TR for the CVT 20 that willapply a load to the engine 18 to force the engine 18 to run atapproximately the target engine speed TES determined at the block 302.The ECM 26 may determine the transmission ratio TR using any appropriatemethod such as those described above.

After determining the target engine speed TES and the transmission ratioTR at the blocks 302, 304, respectively, control passes to a block 306where the ECM 26 transmits transmission command signals to the CVTactuator 32. Upon receiving the transmission command signals, the CVTactuator 32 adjusts the CVT 20 to provide the calculated transmissionratio TR between the transmission output shaft 34 and the engine outputshaft 30. With the CVT 20 creating the transmission ratio TR between theshafts 30, 34, the CVT 20 creates the load on the engine 18 to force theengine 18 to the target engine speed TES. The transmission commandsignals may be the appropriate type of input signals for the particularCVT actuator 32 implemented in the machine 10, such as varying currents,digital control signals or other appropriate control signals such asthose described above.

With the CVT actuator 32 controlling the CVT 20 per the transmissioncommand signals from the ECM 26 to force the engine 18 toward the targetengine speed TES, control may pass to a block 308 where the ECM 26compares the desired engine speed (i.e., target engine speed TES) to theactual engine speed (i.e., engine output speed EOS). By utilizing theengine output speed EOS as the feedback signal, the engine 18 may bemaintained at approximately the target engine speed TES to reduce wearon the engine 18 that can be caused by highly fluctuating engine speeds.After the comparison, control may pass to a block 310 where the ECM 26evaluates whether the engine output speed EOS is too low. In someimplementations, any variation in the engine output speed EOS from thetarget engine speed TES may cause corrective action to be taken to bringthe engine output speed EOS back to the target engine speed TES. Inother implementations, the difference may be required to be greater thana predetermined minimum engine speed error for corrective action tooccur. For example, the difference between the engine output speed EOSand the target engine speed TES may be required to be greater than aspecified number of revolutions per minute or a specified percentage ofthe target engine speed TES for corrective action to occur.

If the ECM 26 determines at the block 310 that the engine output speedEOS is less than the target engine speed TES by more than a minimumengine speed difference, control may pass to a block 312 where the ECM26 may calculate a revised transmission ratio TR that will increase theengine output speed EOS. As shown in the graph 60 of FIG. 3, the enginespeed increases as the load on the engine output shaft 30 decreases.Consequently, the ECM 26 will determine a reduced transmission ratio TRthat will reduce the load on the engine output shaft 30 and allow theengine output speed EOS to increase for the same throttle setting of theengine 18. For a hydrostatic CVT, the reduced transmission ratio TR mayequate to rotating the swash plate of the variable displacement pumptoward a zero flow or neutral position so that the fluid displacementper revolution of the pump input shaft is reduced. For a variablediameter pulley CVT, an input pulley diameter may be decreased and anoutput pulley diameter correspondingly increased to increase the numberof rotations of the input pulley per rotation of the output pulley.Similar adjustments will be determined by the ECM 26 for other types ofCVTs 20. After the ECM 26 determines the reduced transmission ratio TRat the block 114, control may pass back to the block 108 to outputupdated transmission command signals to the CVT actuator 32 to adjustthe transmission ratio TR of the CVT 20.

If the engine output speed EOS is not too slow at the block 310, controlpasses to a block 314 where the ECM 26 determines whether the engineoutput speed EOS is too fast. As discussed above, in variousimplementations, corrective action may be taken any time the engineoutput speed EOS is greater than the target engine speed TES to reducethe engine output speed EOS, or corrective action may be taken if theengine output speed EOS is greater than the target engine speed TES by apredetermined number of revolutions per minute or percentage above thetarget engine speed TES. If the ECM 26 determines that the engine outputspeed EOS is greater than the target engine speed TES by more than aminimum engine speed difference, control may pass to a block 316 wherethe ECM 26 calculates a revised transmission ratio TR that will reducethe engine output speed EOS. Per the graph 60 of FIG. 3, increasing theload on the engine output shaft 30 will reduce the engine output speedEOS. The load on the engine 18 can be increased by increasing thetransmission ratio TR. In a hydrostatic CVT, the swash plate to thevariable displacement pump can be rotated to increase the fluid flowthrough the pump. For a variable diameter pulley CVT, the input pulleydiameter can be increased and the output pulley diameter can becorrespondingly decreased to decrease the number of rotations of theinput pulley per rotation of the output pulley. Other CVTs 20 can beadjusted as necessary to increase the transmission ratio TR. After theECM 26 determines the increased transmission ratio TR to slow down theengine 18 to the target engine speed TES, control may pass back to theblock 306 to transmit the updated transmission command signals to theCVT actuator 32.

If the ECM 26 determines that the engine output speed EOS is equal tothe target engine speed TES, or differs within an acceptable range fromthe target engine speed TES, at the blocks 310, 314, control may passback to the block 102 of the routine 100 to continue receiving andevaluating the engine output commands and the brake force commands fromthe operator input devices 24.

In the preceding discussion of the routine 300, the engine output speedEOS is impliedly the control error for the target engine speed controlroutine 300. Consequently, the engine output speed EOS is directlycompared to the target engine speed TES to determine whether thetransmission ratio TR must be updated to get the engine output speed EOSwithin an acceptable range about the target engine speed TES. Inalternative implementations, the transmission ratio TR can be used asthe control error since the transmission ratio TR is being adjusted tocorrect errors in the engine output speed EOS. In such implementations,the routine 300 may be adjusted to evaluate an actual transmission ratioATR of the CVT 20 relative to a desired transmission ratio DTR todetermine whether to adjust the transmission ratio TR. In the modifiedroutine 300, the desired transmission ratio DTR may be equal to thetransmission output speed TOS measured by the transmission speed sensor52 divided by the target engine speed TES determined by the ECM 26. Theactual transmission ratio ATR is equal to the transmission output speedTOS divided by the engine output speed measured by the engine speedsensor 48.

In this implementation, the routine 300 begins at the blocks 302, 304,306 as described above. At the block 308, the ECM 26 calculates andcompares the desired transmission ratio DTR to the actual transmissionratio ATR instead of directly comparing the engine output speed EOS tothe target engine speed TES. Control then passes to the block 310 todetermine whether the actual transmission ratio ATR is greater than thedesired transmission ratio DTR (i.e., the engine output speed EOS isless than the target engine speed TES, and therefore too slow). If theactual transmission ratio ATR is too high, the engine output speed EOSmust be increased to reduce the actual transmission ratio ATR.Consequently, if the actual transmission ratio ATR is greater than thedesired transmission ratio DTR by a predetermined minimum transmissionratio error, control passes to the block 312 for the ECM 26 to determinea reduced transmission ratio TR that will increase the engine outputspeed EOS and thereby reduce the actual transmission ratio ATR.

If the actual transmission ratio ATR is not greater than the desiredtransmission ratio DTR at the block 310, control passes to the block 314to determine whether the actual transmission ratio ATR is less than thedesired transmission ratio DTR (i.e., the engine output speed is greaterthan the target engine speed TES, and therefore too fast). If the actualtransmission ratio ATR is too low, the engine output speed EOS must bedecreased to increase the actual transmission ratio ATR. If the actualtransmission ratio ATR is too low by more than the predetermined minimumtransmission ratio error, control passes to the block 316 for the ECM 26to determine an increased transmission ratio TR that will decrease theengine output speed EOS and increase the actual transmission ratio ATR.

INDUSTRIAL APPLICABILITY

The apparatus and method of the present disclosure allows for theperformance of CVT transmission control in the machine 10 using reliablefeedback information so that instability is not created while drivingthe machine 10 over a work surface. Under normal operating conditions,the transmission output control strategy may be executed to propel themachine 10 across the work surface according to a desired transmissionoutput torque input by the operator of the machine 10. When conditionsindicate that transmission output feedback signals used in thetransmission output control strategy are unreliable, such as when thebrakes 36 are applied or when the transmission torque sensor 54 fails ormalfunctions, the ECM 26 may adjust to executing the target engine speedCVT transmission control strategy that uses the engine output speedsignal as feedback to control power output and the machine speed of themachine 10 until the conditions causing the unreliability of thetransmission output feedback signals are corrected or otherwiseeliminated.

The method for target engine speed control in accordance with thepresent disclosure utilizes the speed of the engine 18, either directlyor indirectly via the actual transmission ratio TR, to maintain theengine output speed EOS approximately equal to the target engine speedTES determined based on engine output commands from an operator.Previous control strategies utilize the transmission output speed TOS orthe transmission output torque to control cause the machine 10 torespond to the operator's desired machine output. Such controlstrategies provide good resolution on the output torque or the machinespeed in comparison to the operator commands. However, the engine speedfluctuates to accommodate changing driveline efficiencies in the powertrain. In some situations, high fluctuations in engine speeds can causegreater wear in the engine 18 over time. In some implementations,maintaining the engine 18 at as constant an engine speed as possible fordurability and to prolong the life of the engine 18 may be a higherpriority machine requirement than precise control of the speed or torqueat the output of the CVT 20. The control strategy in accordance with thepresent disclosure provides good resolution on the engine speed whileallowing the transmission output speed TOS and the output torque tofluctuate to accommodate the changing driveline efficiencies in thepower train.

While the preceding text sets forth a detailed description of numerousdifferent embodiments, it should be understood that the legal scope ofprotection is defined by the words of the claims set forth at the end ofthis patent. The detailed description is to be construed as exemplaryonly and does not describe every possible embodiment since describingevery possible embodiment would be impractical, if not impossible.Numerous alternative embodiments could be implemented, using eithercurrent technology or technology developed after the filing date of thispatent, which would still fall within the scope of the claims definingthe scope of protection.

It should also be understood that, unless a term was expressly definedherein, there is no intent to limit the meaning of that term, eitherexpressly or by implication, beyond its plain or ordinary meaning, andsuch term should not be interpreted to be limited in scope based on anystatement made in any section of this patent (other than the language ofthe claims). To the extent that any term recited in the claims at theend of this patent is referred to herein in a manner consistent with asingle meaning, that is done for sake of clarity only so as to notconfuse the reader, and it is not intended that such claim term belimited, by implication or otherwise, to that single meaning.

What is claimed is:
 1. A machine for operating at a work site andtraveling over a work surface of the work site, the machine comprising:an engine; a traction device; a continuously variable transmission (CVT)operatively connected between the engine and the traction device totransfer power output by the engine to the traction device; operatorinput devices in an operator station of the machine for detecting engineoutput commands and brake force commands that are input by an operatorof the machine and outputting engine output command signalscorresponding to the engine output commands and brake force commandsignals corresponding to the brake force commands input by the operatorat the operator input devices; a transmission output parameter sensorautomatically monitoring a transmission output parameter of the CVT andoutputting transmission output parameter sensor signals corresponding tothe transmission output parameter of the CVT; an engine speed sensorautomatically monitoring an engine output speed of the engine andoutputting engine speed sensor signals corresponding to the engineoutput speed of the engine; and an electronic control module (ECM)operatively connected to the engine, the CVT, the operator inputdevices, the engine speed sensor and the transmission output parametersensor, wherein the ECM is programmed to: receive the engine outputcommand signals and the brake force command signals from the operatorinput devices, in response to determining that the transmission outputparameter sensor signals from the transmission output parameter sensorare a reliable indicator of transmission output conditions, execute atransmission output control routine based on the engine output commandsignals and the transmission output parameter sensor signals to controla machine output of the machine, and in response to determining that thetransmission output parameter sensor signals from the transmissionoutput parameter sensor are not the reliable indicator of thetransmission output conditions: determine a transmission control targetengine speed based on the engine output command signals, determine atransmission ratio for the CVT based on the transmission control targetengine speed to cause the engine to operate at the transmission controltarget engine speed, and transmit transmission command signals to theCVT to control the CVT so that a transmission output speed divided by atransmission input speed is equal to the transmission ratio determinedbased on the transmission control target engine speed.
 2. The machine ofclaim 1, wherein the ECM determines that the transmission outputparameter sensor signals are not the reliable indicator of thetransmission output conditions by determining that the transmissionoutput parameter sensor is malfunctioning.
 3. The machine of claim 1,wherein the ECM determines that the transmission output parameter sensorsignals are not the reliable indicator of the transmission outputconditions by determining that a commanded brake force in the brakeforce command signals is greater than zero.
 4. The machine of claim 1,wherein the ECM determines that the transmission output parameter sensorsignals are the reliable indicator of the transmission output conditionsby determining that the transmission output parameter sensor isfunctioning properly and a commanded brake force in the brake forcecommand signals is equal to zero.
 5. The machine of claim 1, wherein theECM is programmed to, in response to determining that the transmissionoutput parameter sensor signals from the transmission output parametersensor are not the reliable indicator of the transmission outputconditions: receive the engine speed sensor signals from the enginespeed sensor and compare the engine output speed from the engine speedsensor signals to the transmission control target engine speed, andcalculate a revised transmission ratio that will cause the engine outputspeed to be approximately equal to the transmission control targetengine speed and transmit revised transmission command signals to theCVT to control the CVT to the revised transmission ratio in response todetermining that the engine output speed is not equal to thetransmission control target engine speed.
 6. The machine of claim 5,wherein the ECM is programmed to calculate the revised transmissionratio to be less than the transmission ratio in response to determiningthat the engine output speed is less than the transmission controltarget engine speed.
 7. The machine of claim 5, wherein the ECM isprogrammed to calculate the revised transmission ratio to be greaterthan the transmission ratio in response to determining that the engineoutput speed is greater than the transmission control target enginespeed.
 8. The machine of claim 5, comprising a transmission speed sensoroperatively connected to the CVT and the ECM and automaticallymonitoring the transmission output speed of the CVT and outputtingtransmission speed sensor signals corresponding to the transmissionoutput speed of the CVT, wherein the ECM is programmed to calculate adesired transmission ratio that is equal to the transmission outputspeed divided by the transmission control target engine speed, andcalculate an actual transmission ratio that is equal to the transmissionoutput speed divided by the engine output speed.
 9. The machine of claim8, wherein the ECM is programmed to: calculate the revised transmissionratio to be less than the transmission ratio in response to determiningthat the actual transmission ratio is greater than the desiredtransmission ratio; and calculate the revised transmission ratio to begreater than the transmission ratio in response to determining that theactual transmission ratio is less than the desired transmission ratio.10. The machine of claim 8, wherein the ECM is programmed to: calculatethe revised transmission ratio to be less than the transmission ratio inresponse to determining that the actual transmission ratio is greaterthan the desired transmission ratio by more than a predetermined minimumtransmission ratio error; and calculate the revised transmission ratioto be greater than the transmission ratio in response to determiningthat the actual transmission ratio is less than the desired transmissionratio by more than the predetermined minimum transmission ratio error.11. A method for controlling an engine output speed of an engine of amachine, wherein the machine includes a traction device and acontinuously variable transmission (CVT) operatively connected betweenthe engine and the traction device to transfer power output by theengine to the traction device to propel the machine over a work surfaceof a work site, the method comprising: receiving engine output commandsignals and brake force command signals from an operator of the machineindicating a commanded machine function and a commanded brake force,respectively, input by the operator; in response to determining thattransmission output parameter sensor signals are a reliable indicator oftransmission output conditions, performing a transmission output controlroutine based on the engine output command signals and the transmissionoutput parameter sensor signals to control a machine output of themachine; and in response to determining that the transmission outputparameter sensor signals are not the reliable indicator of thetransmission output conditions: determining a transmission controltarget engine speed based on the engine output command signals,determining a transmission ratio for the CVT based on the transmissioncontrol target engine speed to cause the engine to operate at thetransmission control target engine speed, and transmitting transmissioncommand signals to the CVT to control the CVT so that a transmissionoutput speed divided by a transmission input speed is equal to thetransmission ratio determined based on the transmission control targetengine speed.
 12. The method of claim 11, comprising determining thatthe transmission output parameter sensor signals are not the reliableindicator of the transmission output conditions by determining that atransmission output sensor transmitting the transmission outputparameter sensor signals is malfunctioning.
 13. The method of claim 11,comprising determining that the transmission output parameter sensorsignals are not the reliable indicator of the transmission outputconditions by determining that the commanded brake force in the brakeforce command signals is greater than zero.
 14. The method of claim 11,comprising determining that the transmission output parameter sensorsignals are the reliable indicator of the transmission output conditionsby determining that a transmission output sensor transmitting thetransmission output parameter sensor signals is functioning properly andthe commanded brake force in the brake force command signals is equal tozero.
 15. The method of claim 11, comprising, in response to determiningthat the transmission output parameter sensor signals are not thereliable indicator of the transmission output conditions: comparing theengine output speed of the engine to the transmission control targetengine speed; and calculating a revised transmission ratio that willcause the engine output speed to be approximately equal to thetransmission control target engine speed and transmitting revisedtransmission command signals to the CVT to control the CVT to therevised transmission ratio in response to determining that the engineoutput speed is not equal to the transmission control target enginespeed.
 16. The method of claim 15, comprising calculating the revisedtransmission ratio to be less than the transmission ratio in response todetermining that the engine output speed is less than the transmissioncontrol target engine speed.
 17. The method of claim 15, comprisingcalculating the revised transmission ratio to be greater than thetransmission ratio in response to determining that the engine outputspeed is greater than the transmission control target engine speed. 18.The method of claim 15, comprising calculating a desired transmissionratio that is equal to the transmission output speed divided by thetransmission control target engine speed, and calculating an actualtransmission ratio that is equal to the transmission output speeddivided by the engine output speed.
 19. The method of claim 18,comprising: calculating the revised transmission ratio to be less thanthe transmission ratio in response to determining that the actualtransmission ratio is greater than the desired transmission ratio; andcalculating the revised transmission ratio to be greater than thetransmission ratio in response to determining that the actualtransmission ratio is less than the desired transmission ratio.
 20. Themethod of claim 18, comprising: calculating the revised transmissionratio to be less than the transmission ratio in response to determiningthat the actual transmission ratio is greater than the desiredtransmission ratio by more than a predetermined minimum transmissionratio error; and calculating the revised transmission ratio to begreater than the transmission ratio in response to determining that theactual transmission ratio is less than the desired transmission ratio bymore than the predetermined minimum transmission ratio error.